I haven't managed reproduce this on my local box, but here my thoughts about the issue:
I believe this failure happens because of race on port 1234 between AddressSanitizer-i386-linux and AddressSanitizer-x86_64-linux instances of recvfrom.cc testcase. This patch tries to resolve the issue by trying to use another port if 1234 has already acquired.

That way, even though we're slightly more noisy when there's no error (and with the CHECK lines), you should immediately see the proper error string when the test fails, since FileCheck will fail on that line.
(Then again, FileCheck might show the appropriate line already, so no need to switch that part (except for perror).